Become a fan of Slashdot on Facebook

 



Forgot your password?
typodupeerror
×
Earth Science

Splitting Water For Fuel While Removing CO2 From the Air (arstechnica.com) 247

An anonymous reader quotes a report from Ars Technica: A new study led by the University of California, Santa Cruz's Greg Rau highlights another tool for our CO2 removal toolbox: splitting seawater to produce hydrogen gas for fuel while capturing CO2 with ocean chemistry. In electrolysis, a device powered by electricity is used to split H2O, producing hydrogen gas. Several chemical modifications to this process have been proposed that can also grab CO2 from the atmosphere. Like the idea of using biofuels, this represents a "win-win" by producing an energy resource while capturing CO2, bringing the cost down. [T]he gist is that atmospheric CO2 goes into the ocean as bicarbonate -- which won't acidify the water or harm ecosystems. So if you power the electrolysis process with renewable energy, you can turn solar/wind/hydroelectric energy into hydrogen fuel while also removing CO2 from the air.

The new study focuses on a basic estimate of the cost and maximum potential of this technique. First, the researchers worked out its efficiency of CO2 capture -- about 0.3 tons captured per gigajoule of electricity input, including the losses from quarrying and crushing rock. That's around 10 times greater than biofuel schemes, but it depends on the assumption that there is demand for all the hydrogen fuel you make. The hydrogen can be used by vehicles, and there's the possibility of using hydrogen as a type of storage for the electric grid -- using excess power to make hydrogen that can run a power plant when needed. So it's not too farfetched that demand could rise to meet supply. The researchers' back-of-the-envelope estimate puts the cost of this system at between $3 and $161 per ton of captured CO2, depending on which type of renewable energy powers it.
The study has been published in the journal Nature Climate Change.
This discussion has been archived. No new comments can be posted.

Splitting Water For Fuel While Removing CO2 From the Air

Comments Filter:
  • Bad Chemistry (Score:5, Insightful)

    by methano ( 519830 ) on Thursday June 28, 2018 @10:44PM (#56863366)
    The gist that atmospheric CO2 goes into the ocean as bicarbonate and won't acidify the water is not correct.
    • Re:Bad Chemistry (Score:5, Informative)

      by divide overflow ( 599608 ) on Friday June 29, 2018 @01:22AM (#56863742)
      (Re)read the article, particularly the fifth paragraph:

      For example, one method uses special membrane filters to separate the hydrogen and hydroxide ions produced during electrolysis. Adding the hydroxide to water allows it to take up CO2 from the air, turning it into bicarbonate. If the hydrogen ions weren't separated, they'd push the chemical equilibrium away from bicarbonate and toward dissolved CO2. But when powdered carbonate rock is added, it can react with the dissolved (atmospheric) CO2 to produce a bunch of happy, stable bicarbonate. Combined, these reactions allow people to tune the hydrogen production and carbonate formation.

      The CO2 is not being dissolved into the water to form carbonic acid, it is being added to hydroxide ions produced by electrolysis to form soluble alkaline bicarbonates.

      • by nospam007 ( 722110 ) * on Friday June 29, 2018 @01:43AM (#56863774)

        "The CO2 is not being dissolved into the water to form carbonic acid, it is being added to hydroxide ions produced by electrolysis to form soluble alkaline bicarbonates."

        And it will bind itself to the acid water and create CO2 and we'll get a bubbly ocean.

        • Re:Bad Chemistry (Score:4, Informative)

          by divide overflow ( 599608 ) on Friday June 29, 2018 @01:51AM (#56863788)
          When you bind the dissolved carbonic acid to hydroxides produced by electrolysis it neutralizes the acid.
          • I see someone has never had a fish tank. While you're technically correct, aquatic life tends to survive alkalinity about as well as acidity.
            • by G00F ( 241765 )

              while your average fish tank creature might not show signs of this being a problem, it certainly does make it so most cannot reporduce.

              From eggs not being able to be fertilized, to the creatures not wanting to mate.

              • well... "about as well as" not very well is still not very well, so... yes, that was what I was getting at
        • We'll get an equilibrium. Some of it will react as you describe. Some of it won't. It depends on exactly how much bicarbonate we are shoving into how much ocean.

      • Re:Bad Chemistry (Score:4, Interesting)

        by methano ( 519830 ) on Friday June 29, 2018 @06:57AM (#56864534)
        How am I getting a zero and this guy is getting a five. You can't dissolve the CO2 into water without adding a bunch of rock to it. A lot of rock. It's probably more efficient just spreading the rock out on the ground and letting it suck the CO2 out of the air. You guys are coders and don't know crap about chemistry. Balance those equations.
        • There is a difference between a software dev/eng and a code monkey.
        • I really don't need to balance any equations. If it sounds to good to be true then it probably is.

          Firstly hydrogen as a fuel source is more dangerous than a lot of other alternatives both in use and transport. Secondly in order to produce a sufficient amount to support replacing fossil fuels I don't think it matters if it does or doesn't raise the pH of the water that's a lot of CO2 and a change to the environment which will still have an impact on the marine life.

          • I'm as much of a skeptic as you are, but if you create the hydrogen near the point that it will be used (i.e. right next to a gas turbine), you can solve a lot of safety issues. Raising the pH of the ocean is a problem. But right now it is acidifying to to atmospheric CO2, so this may be a net win if we only raise it back to "normal" levels.
          • Re:Bad Chemistry (Score:4, Informative)

            by Green Mountain Bot ( 4981769 ) on Friday June 29, 2018 @11:10AM (#56865900)
            And hydrogen isn't even a fuel source - it's a fuel store. It takes more energy to produce hydrogen than the hydrogen itself provides when used. It might be useful for getting around transmission loss over long distances, but it's definitely not a source itself and should not be treated as such in energy policy.
  • In electrolysis, a device powered by electricity is used to split H2O, producing hydrogen gas.

    Yes but does it scale?

    • by whoever57 ( 658626 ) on Thursday June 28, 2018 @11:25PM (#56863464) Journal

      Yes but does it scale?

      From the sub-heading of TFA:
      "Technique could be practical enough to scale."

      • That, of course, is a maybe (and likely not), and not a yes. If you think I'm wrong, you can loan me a million dollars and I could pay you back.
        • "could be" doesn't indicate something is unlikely... at least not without inflection in the speakers tone.
          • "could be" doesn't indicate something is unlikely...

            No. But, in this case, a basic understanding of thermodynamics does.

            • No, a basic understanding of thermodynamics indicates it isn't net energy positive but since the point is to sequester CO2 not be energy positive it doesn't really matter.
              • If you take into account the effect massive-scale desalinization would have on the ocean as a whole and the local environments around the desalinization plants, you quickly begin to understand why it quite likely cannot scale. When you factor in the bicarbonate increasing the alkalinity of the ocean and killing off oceanic life (alkalinity is just as bad as acidity, it's pretty basic -- no pun intended), it becomes obvious.

                We're talking about electrical energy, heat energy, and chemical energy so, yes, al
  • Too early (Score:5, Insightful)

    by religionofpeas ( 4511805 ) on Thursday June 28, 2018 @11:33PM (#56863484)

    If you're generating electricity, it's much more efficient to use that to charge electric cars, and reduce the amount of CO2 that goes into the atmosphere, rather than using inefficient methods to get it out.

    Also, hydrogen fuel is a dumb idea. There is no infrastructure, conversion/storage is inefficient and it makes metals brittle. It's much better to focus on electric battery cars.

    • Re: Too early (Score:5, Insightful)

      by c6gunner ( 950153 ) on Thursday June 28, 2018 @11:43PM (#56863516) Homepage

      If you're generating electricity, it's much more efficient to use that to charge electric cars, and reduce the amount of CO2 that goes into the atmosphere

      It depends on what your goals are. Even without looking at their numbers I can safely guess that this will be less efficient and therefore more expensive than just using batteries. So if your goal is to have the cheapest low-emission energy possible then yeah, batteries are better. On the other hand, if you're more worried about recapturing some of the carbon we've emmited over the last century or two and are willing to paya bit more towards that goal, then this technique might make more sense.

      Whether or not it makes sense even in the latter scenario will depend on just how much more expensive it happens to be. We won't know that until they've done a lot more work on this tech.

      • Re: Too early (Score:5, Insightful)

        by religionofpeas ( 4511805 ) on Thursday June 28, 2018 @11:54PM (#56863552)

        That's why I said "too early". While we still have most cars producing CO2 from fossil fuels, it makes no sense to start recapturing. Recapturing combines an inefficient process at one end (cars generate a lot of CO2 for little energy output) using an inefficient process at the other end (use a lot of energy to recapture a small amount of CO2).

        When all the low hanging fruit is gone, we can start worrying about recapture, preferably using a process that produces something more useful than hydrogen.

      • regardless - who or how would this be paid for? taxes = no.
    • Re: (Score:3, Informative)

      by Anonymous Coward

      In order to avoid 2C of warming by 2100, we need to have negative annual CO2 emissions by 2050. That's on the most optimistic trajectories, too. More pessimistic ones say we've already locked in 2C of warming, and negative emissions by 2050 are required to avoid 4C of warming by 2100.

      In other words, moving to electric cars by itself is not going to produce the negative CO2 emissions that we need. This sort of technology, in conjunction with electrics cars, could.

      • In order to avoid 2C of warming by 2100, we need to have negative annual CO2 emissions by 2050

        That may be true, but it will be challenging enough to convert most of our ICE vehicles to electric by 2050.

      • Can we get off cars?
        Sure Car pollution is a big problem. It is also what we feel the most, having to fuel up our cars.
        But they are other problems too. Our homes which we are often not in for 8-16 hours a day, which is still being heated or cooled, while we spend time in other building that are being heated or cooled then we leave for home having this building not occupied.
        While we may pay for metered electricity, the power plants cant just drop their generation by 0.000001% when you turn off your light when

        • Can we get off cars? Sure Car pollution is a big problem. It is also what we feel the most, having to fuel up our cars. But they are other problems too.

          A good point.

          Cars are one of the many systems in our culture producing carbon dioxide from fossil fuels. But there are many others.

        • >While we may pay for metered electricity, the power plants cant just drop their generation by 0.000001% when you turn off your light when you go to bed. They are still generating power.

          Actually, no. When you turn off your light he power company does indeed need to reduce its production accordingly, unless they have battery buffers involved somewhere. Every watt flowing into the system *will* flow back out again - as heat buildup and exploding infrastructure if nothing else. And the power company tend

    • If you're generating electricity, it's much more efficient to use that to charge electric cars, and reduce the amount of CO2 that goes into the atmosphere, rather than using inefficient methods to get it out.

      Cool you've solved cars. ... Now what? If you target a single group of emissions we won't ever achieve our goal of a cleaner future.

    • by zieroh ( 307208 )

      Also, hydrogen fuel is a dumb idea. There is no infrastructure, conversion/storage is inefficient and it makes metals brittle. It's much better to focus on electric battery cars.

      Hydrogen may (or may not) be a viable form of energy storage. Infrastructure, though, is perhaps the weakest argument against it. First, some of the infrastructure is already in place -- there are two hydrogen filling stations near my house for use by the hydrogen-powered cars that are already on the market. So there's that.

      Second, you can make hydrogen (inefficiently, at present) with water and electricity.

      You know what kind of infrastructure is really well developed in the world? Water and electricity.

    • Long before you start generating surplus hydrogen that you could use as fuel, you'll be generating hydrogen for industrial purposes. So no, it's not a dumb idea to find better ways to generate hydrogen because we need it to run our civilization anyway, even if we'll all drive BEVs.
    • What's not mentioned in the summary is that aside from not harming the oceans with bicarbonate, it also might actually help by accelerating the amount of bicarbonate in the ocean that is already caused by natural weathering. Overall in a few generations this could prevent too much ocean acidification and thus prevent too much damage to the oceans from other acid sources.

      For example, see House et al, "Electrochemical acceleration of chemical weathering as an energetically feasible approach to mitigating anth

    • by Swistak ( 899225 )
      You say "electric" and "battery" as if that electricity came from air. It does not, in most countries it comes from burning coal.
      So first we burn coal to generate electricity (with loses), then we transmit electricity (up to 40% of losses on power lines), then we charge the batteries (again some small loses), then we transform electricity into motion (again with loses).

      How about we burn fuel and we transform it directly into motion? (with loses of course, but much smaller).

      EV cars are "green" only if y
      • by sjbe ( 173966 )

        You say "electric" and "battery" as if that electricity came from air. It does not, in most countries it comes from burning coal.

        For now that is true. But you seem to be forgetting that with EVs we gain the option to change that fact. I can and have charged an EV from solar generated electricity. We use coal fired plants because 40 years ago that was the only realistic option in many places. Times have changed and our cars need to change with them. Internal combustion engines are a technological and environmental dead end. We've ridden that horse as far as it will take us. Time to switch to a fresh new ride.

        So first we burn coal to generate electricity (with loses), then we transmit electricity (up to 40% of losses on power lines), then we charge the batteries (again some small loses), then we transform electricity into motion (again with loses).

        Powerline loses are

      • You say "electric" and "battery" as if that electricity came from air. It does not, in most countries it comes from burning coal.

        Wow! What an untruth about "in most countries it comes from burning coal." Clearly you don't live in France (75% Nuclear) or Norway (98% Hydroelectric). In many European counties Natural Gas fired power stations are dominant over coal such as in the UK where coal is on its last legs (will be gone by 2025). There are countries such as Poland that have a high level of coal usage for producing electricity.

    • Your arguments against Hydrogen fuel seems a bit week.
      No Infrastructure: If deemed a viable energy source one can be built. Normal Oil companies would probably like that idea, converting gas station to hydrogen stations. Unlike solar or "Home grown" or Grid energy they can keep their business model. They just change the energy source.
      Conversion is ineffective: Efficiencies is rather over rated concept. Especially if you can be inefficient for cheap.
      Storage makes metals brittle: Too bad we don't have othe

  • by Anonymous Coward on Friday June 29, 2018 @12:10AM (#56863582)

    To possibly produce jet fuel from sea water [huffingtonpost.com] on aircraft carriers while underway. In addition to obtaining hydrogen and oxygen from electrolysis of sea water you also liberate some of the carbon dioxide that's dissolved in solution as part of that sea water. The combination of hydrogen, oxygen and carbon dioxide can, with sufficient energy input, most likely from the nuclear reactors [wikipedia.org] that power the ship, be converted to a mixture of carbon monoxide, hydrogen and some carbon dioxide in a mixture known as SynGas or "synthesis gas" [wikipedia.org]. From there it can be converted via the Fischer Tropsch Process [wikipedia.org] into heavier hydrocarbons and eventually into a mixture of longer chain hydrocarbons approximating JP-5 jet fuel [wikipedia.org].

    Why aren't we already doing this on land you might ask? Well, in a word, because it's expensive in both industrial plant and equipment and also from an energy input perspective. Much more expensive than simply pumping crude oil out of the ground and refining it. However, that matters less on a ship underway at sea, away from land supplies, and with nuclear energy to spare where cost is less of a factor than ease of supply, which is militarily advantageous.

    • by crow ( 16139 )

      I heard about that. One scenario that they were looking at was putting a small nuclear reactor (like you would find in a submarine) at a base in Afghanistan and produce diesel-compatible fuel. Sure, the cost would be huge, but you would eliminate the need for lots of trucks that are being shot at. Obviously they would have to secure the reactor, as it would be a high priority target, but reducing dependencies on supply lines is a massive logistical win.

      Generating fuel with excess electricity on an aircra

  • by u19925 ( 613350 ) on Friday June 29, 2018 @12:49AM (#56863668)

    "cost of this system at between $3 and $161 per ton of captured CO2". With a range like this, who wants to read the article?

  • by Martin S. ( 98249 ) on Friday June 29, 2018 @01:01AM (#56863692) Journal

    If renewable energy such as off-shore wind farms were used we could achieve carbon neutral hydro-carbon fuel, we could even pump the spare fuel into natural crude oil reservoirs for carbon capture.

    We get to keep our gas guzzlers with a clear conscience.

  • this is publishable? (Score:5, Informative)

    by Goldsmith ( 561202 ) on Friday June 29, 2018 @01:37AM (#56863762)

    I wish I'd known this was publishable. I wrote up a report on this years ago while working for the Navy... they actually funded someone to try this out, I think.

    Short version: it's expensive. Slightly longer version: chlorine is a problem. If you think you're electrochemically evolving hydrogen gas strait from sea water, you're probably just going to kill a lot of people instead. Catalysts are the answer. Bonus detail: the ocean (for a few reasons) concentrates carbon. There's a lot of carbon in there, and the core of this idea is very good.

    • I wish I'd known this was publishable.

      Everything is publishable. You just have to convince someone to publish it.

      while working for the Navy

      Or more importantly you'll need to convince people to LET you publish it.

  • by ukoda ( 537183 ) on Friday June 29, 2018 @03:24AM (#56864032) Homepage
    Hydrogen powered cars have annoyed me for years as I am convinced are not practical and mainly funded to muddy the waters around the development of pure EVs. However if this was used for grid storage it could be a practical idea. Make hydrogen when you have surplus renewable energy and burn it at the same location when you need to support the grid. No issues with transport or storage density and you could locate it a bit away from population centers if you worry about safety.

    As much as I love Tesla I feel using Li-Ion batteries for grid storage is a bad idea as you don't have the same space/weight concerns for grid storage that you do in an EV and therefore such batteries are better deployed for EVs where they bring the most benefit.
    • Hydrogen powered cars have annoyed me for years as I am convinced are not practical and mainly funded to muddy the waters around the development of pure EVs.

      Certainly. They aren't a terrible idea but the fueling infrastructure problem alone pretty much dooms hydrogen fuel cells to power cars before they even get started. BEVs have their problems too but they have the one HUGE advantage that there already is a fuel infrastructure (the electric grid) in place. Needs some upgrades but we're not starting from scratch.

      As much as I love Tesla I feel using Li-Ion batteries for grid storage is a bad idea as you don't have the same space/weight concerns for grid storage that you do in an EV and therefore such batteries are better deployed for EVs where they bring the most benefit.

      The flaw in your logic there is that you are presuming using Li-Ion batteries in cars somehow precludes their use in grid applications. In reality

      • Unfortunately, as soon as electric cars start going mainstream, they will easily consume all available production for decades - we can always build more battery production plants (and recycling - that's going to be a huge factor too), but the economies of scale will begin to diminish rapidly. And it's not at all clear that there's enough lithium on the planet to satisfy the demand for a global conversion to EVs, especially if harvested in an ecologically responsible manner.

        Using Li-Ion batteris for the gri

        • Unfortunately, as soon as electric cars start going mainstream, they will easily consume all available production for decades - we can always build more battery production plants (and recycling - that's going to be a huge factor too), but the economies of scale will begin to diminish rapidly.

          That could only be true if there was a limitation on some of the components. And even if your scenario did play out that's not actually a problem as far as grid utilization goes. We don't HAVE to use Li-Ion for grid applications if there is enough demand elsewhere (cars etc) to get to minimum efficient scale.

          And it's not at all clear that there's enough lithium on the planet to satisfy the demand for a global conversion to EVs, especially if harvested in an ecologically responsible manner.

          There is quite a lot of lithium according to the USGS. The problems for the next several decades will be most likely a series of short term shortages while we fully utilize existing sources and have

      • I think you are seriously overstating the problem... we already have a network of fueling stations everywhere that can distribute hydrogen instead of or in addition to gasoline.
        • I think you are seriously overstating the problem... we already have a network of fueling stations everywhere that can distribute hydrogen instead of or in addition to gasoline.

          No we do not. Not on the sort of scale needed to actually get the general public to actually buy hydrogen powered vehicles anyway. Converting existing gas stations is a HUGE expense with a difficult chicken and egg problem. No gas station is going to install a hydrogen pump without there first being hydrogen powered cars. Nobody is going to buy a hydrogen powered car until the fuel infrastructure is already available. So unless you plan to convince the government to subsidize the problem it just isn't

  • A new study led by the University of California, Santa Cruz's Greg Rau highlights another tool for our CO2 removal toolbox: splitting seawater to produce hydrogen gas for fuel while capturing CO2 with ocean chemistry.

    So what? That's nifty and all but the obstacle to doing any of this is COST. It doesn't really matter what we can do if we cannot do it economically.

    • It isn't all about cost. Are we forgetting our economic system, globally, is entirely based on money we pull out of air and regulate purely on subjective valuations. If we are talking about planet saving technology we tell the independent banking system creating the money to fuck itself and declare the effort free.
  • by Rick Schumann ( 4662797 ) on Friday June 29, 2018 @08:53AM (#56865054) Journal
    We need to stop 'burning' anything and everything. Electric and nuclear/solar/wind are the way forward.
  • I will be amazed if the study took into account the cost of installing renewable energy generation, both in monetary and environmental terms, because these studies literally never do. They always sound great at first glance, and they certainly get their authors a fuckton of grant money but, in the end, someone finally puts two and two together and the idea gets scrapped.

    For example, an array of solar panels big enough to be used for massive-scale desalinization would likely put out more CO2 during the pro
    • "a portion of the solid byproduct of ocean electrolysis is a group of pure acids, which would likely find their way back into the ocean. "

      The article did address this.

      The ideal solution is probably to use nuclear and freeze the output water rather than putting back into the ocean. Just do the whole process at the poles.
      • Right, because freezing water doesn't use energy or give off heat. Oh, and that ice will certainly never melt. Also, the conductivity of near-freezing water found at the poles is lower than at, say, the California coastline, which means it requires more energy to electrolyze; by a substantial amount.

        Did TFA address that?
  • If I burn the hydrogen + oxygen, say in a kiln or furnace, would the net cost per thermal units be cheaper then burning natural gas or propane?

"If there isn't a population problem, why is the government putting cancer in the cigarettes?" -- the elder Steptoe, c. 1970

Working...